Among multiple rotation encoders there are those having magnetic rotating bodies—referred to as multiple rotation detection ring magnets—for the purpose of detecting one or more rotations, in addition to a structure for detecting the displacement within a single rotation, as described, for example, in Japanese Examined Patent Application Publication No. 6-41853. The multiple rotation encoder provides an optical absolute value encoder that detects the absolute angle within a single rotation, and a magnetic encoder for detecting multiple rotations. The optical absolute value encoder that detects the absolute angle within a single rotation is mounted on a shaft 1, and includes a rotating disk 2 for the purpose of detecting the absolute angle within a single rotation, an LED 4 for projecting light on rotating disk 2, an anchoring slit 5, a photodiode array 6 of light-receiving elements, a waveform shaping circuit for waveform shaping of detection signal therefrom into rectangular waves. The magnetic encoder for the purpose of detecting multiple rotations includes: a rotating disk 81 that is equipped with a magnet 82, referred to as a ring magnet, in the rotating part; a magnetoresistive element 9 for the purpose of detecting the number of rotations thereof; a waveform shaping circuit 10; and a control circuit for the purpose of counting the multiple rotation detection signals, and retaining the numeric values thereof.
The magnetoresistive element 9 is able to detect a single rotation by detecting changes in magnetic polarity when magnetic poles are reversed during a single rotation of the ring magnet 82. The structures and mounting positions of such optical system and magnetic system parts in encoders may have a variety of arrangement according to the type of encoder.
The magnetic pattern, whereby magnetic poles are reversed during a single rotation of the ring magnet, is magnetized in accordance with methods described, for example, in Japanese Published Patent Application No. 63-182808 and Japanese Published Patent Application No. 2002-353029. The magnetizing methods all involve magnetizing in the state of a single ring magnet, and the magnetized ring magnet is thereafter attached to the rotary shaft of the encoder. Position determination is performed by, for example, matching a mark for determining position attached to the ring magnet with a mark for determining the position of the encoder rotary shaft.
However, it is believed to be difficult to perform attachment operations while confirming the position determination marks, and there are believed to be frequent variances in the position of the attached ring magnet. There also believed to be a need to improve operational efficiency, since there is believed to have been a great burden on workers.